1. Field of the Invention
The present invention relates to an engine automatic stop and restart apparatus which automatically stops an engine when an automatic stop condition is satisfied, and restarts the engine when a restart condition is satisfied, thereafter.
2. Description of the Related Art
Recently, there is developed an engine automatic stop and restart apparatus for the purpose of improving fuel consumption of an automobile and reducing environmental load, in which when a driver's operation satisfies a predetermined condition for stopping an engine (for example, a pedaling operation of a brake pedal when a vehicle is moving at a speed lower than a predetermined speed), fuel supply is automatically cut off so that the engine is automatically stopped, and after that, when a driver's operation satisfies a predetermined condition for restarting the engine (for example, a releasing operation of the brake pedal, a pedaling operation of an accelerator pedal, and the like), fuel injection is restarted so that the engine is automatically restarted.
Conventionally, there is proposed the following engine automatic stop and restart apparatus (see, for example, Japanese Patent Application No. 2010-033545 filed on Feb. 18, 2010). Specifically, when starting an engine restart process after idling stop, it is judged whether or not self-resumption (restart) can be performed by restarting fuel supply based on an rpm of the engine. When it is judged that the self-resumption can be performed, the engine is restarted only by supplying a fuel without using a starter motor. On the contrary, when it is judged that the self-resumption cannot be performed by itself, supply of electricity to the starter motor is started, connection between a pinion gear and a ring gear is started along with synchronization between the rpm of the starter motor and the rpm of the engine, the connection between the pinion gear and the ring gear is completed when the rpm of the starter motor (that means rpm of the pinion gear, and the same is true in the description below) and the rpm of the engine are synchronized with each other, with the result that the starter motor drives the engine. When it is judged that the engine can be self-resumed, the pinion gear and the ring gear are disconnected.
In this engine automatic stop and restart apparatus described in the related application (Japanese Patent Application No. 2010-033545), the engaged state between the pinion gear and the ring gear is realized before the engine rotation is completely stopped. Therefore, quick restart of the engine can be performed. In addition, when it is judged that the self-resumption can be performed only by supplying the fuel, rotation of the starter motor is stopped even if the starter motor has started to rotate so as to restart the engine only by supplying the fuel. Therefore, use frequency of the starter motor can be reduced, thereby being capable of reducing energy consumption.
In the apparatus described in the above-mentioned related application, as illustrated in FIG. 13, the engine is automatically stopped at time t1, and after that restart of the engine is started at time t2 when it is judged that the rpm of the engine cannot be self-resumed. Then, supply of electricity to the starter motor is started, the connection between the pinion gear and the ring gear is started at time t3, and the connection is completed at time t4. After that, combustion of the engine causes an increase of the rpm of the engine at time t5. The increase of the rpm of the engine is counted by a combustion judgment counter. When a value of the combustion judgment counter becomes above a self-resumption judgment threshold value at time t6, it is judged that the engine is self-resumed. Then, the pinion gear and the ring gear are disconnected, and supply of electricity to the starter motor is stopped. However, if the combustion of the engine is unstable, when it is judged that the engine is self-resumed to disconnect the pinion gear and the ring gear and stop supply of electricity to the starter motor, a restart error may occur. In other words, there is a problem that an engine stop may occur because the engine and the starter motor are disconnected despite that the engine is not self-resumed.
Therefore, in the related application, there is also provided a method of reducing a restart error by setting the self-resumption judgment threshold value for judging the self-resumption of the engine to a larger value when restarting in a low speed region of the rpm of the engine so that the starter motor is driven until the rpm of the engine becomes an rpm of the self-resumption even if the combustion of the engine is unstable. However, as illustrated in FIG. 14, after the engine is automatically stopped at time t1, the restart of the engine is started at time t2 when it is judged that the rpm of the engine cannot be self-resumed. Then, supply of electricity to the starter motor is started, the connection between the pinion gear and the ring gear is started at time t3, and the connection is completed at time t4. After that, combustion of the engine causes an increase of the rpm at time t5. The increase of the rpm of the engine is counted by the combustion judgment counter. Even if the combustion of the engine becomes stable after time t5 and the engine is self-resumed without being driven by the starter motor, when the self-resumption judgment threshold value is set to a large value, the connection between the pinion gear and the ring gear is maintained and the supply of electricity to the starter motor is performed until a value of the combustion judgment counter becomes above the self-resumption judgment threshold value at time t6. Thus, there is a problem that wasteful energy is consumed.